Photoacoustic imaging of a pre-clinical tumour model with an ExactVu micro-ultrasound system

Photoacoustic imaging using a micro-ultrasound system adds physiological information to high-resolution ultrasound images. This work demonstrates the in vivo imaging capability of a combined micro-ultrasound photoacoustic imaging system. A photoacoustic adapted, 22.5 MHz, 512-element transrectal ultrasound system was used to image human prostate cancer (PC3) grown on the hind limb of a nude mouse. Both endogenous chromophores i.e., oxygenated, and deoxygenated hemoglobin and an exogenous biocompatible photoacoustic contrast agent called porphysome nanoparticles were imaged in vivo. Spectral unmixing was used to separate the photoacoustic signals from oxygenated, deoxygenated hemoglobin and porphysomes. Longitudinal imaging with porphysomes revealed that the photoacoustic signal from contrast agent peaks at 6 hours after the injection and degrades gradually potentially due to disassociation of the particle in vivo.